In agricultural use of fertilizers including more specifically, horticultural use, consideration must be given not only to the proper concentrations of “major” nutrients (macronutrients) such as nitrogen (N), phosphorus (P), potassium (K), but also to the situation-dependent need for calcium (Ca) and magnesium (Mg) and the so-called “trace” elements (micronutrients). These latter may include: Iron, manganese, zinc, cadmium, copper, aluminum, silicon, barium, titanium, molybdenum, boron, sodium, sulphur, cobalt, etc. on the rough order of 5-50 ppm.
In preparing a solid fertilizer mix or a concentrated or dilute liquid mix, the individual and mutual water solubilities of these various elements and their compounds must be considered.
To solubilize many of the micronutrients and to keep them in solution in the face of tendencies to precipitate in the presence of elements or compounds with which they may tend to form insoluble precipitates, resort has been made to enhancing the solubility by forming complexes or chelates with appropriate sequestering agents. These may be, for example, N-carboxylalkyl-amino acids, [such as the preferred ethylenediaminetetraacetic acid (EDTA)] and their alkali metal or ammonium salts.
Other complexing or chelating agents are well known in the art, such as those set out in Meyer, U.S. Pat. No. 4,319,910, issued Mar. 16, 1982 (see column 4, lines 21-63); Leutner et al., U.S. Pat. No. 4,395,273, issued Jul. 26, 1983; Kimbro, U.S. Pat. No. 4,425,149, issued Jan. 10, 1984; Rubin, U.S. Pat. No. 3,245,776, issued Apr. 12, 1966; all of which are hereby incorporated by reference).
Even with known use of sequestering agents to solubilize micronutrients, precipitation problems have been experienced, especially when the nutrient situation requires inclusion in the fertilizer of significant concentrations of calcium or magnesium and their compounds, and when a solid or concentrated liquid fertilizer is mixed with locally available water which happens to contain high concentrations of, e.g., calcium and/or magnesium (“hard” water).
In both cases, low solubility salts form, which result in sludge in the mixing vats and scale on the tubes and injectors which feed fertilizer to the plants. They also lock up the nutrient value of the compounds of the precipitate, reducing the economic value of the fertilizer.
Prior attempts to deal with their problems have involved feeding at separate times those nutrients which would precipitate, or attempting to control the pH at all stages to discourage precipitation. A relatively recent attempt to solve this long-standing problem by a variation of the latter approach, using very low pH, and no chelation, is disclosed in Vetanovetz and Peters, U.S. Pat. No. 5,171,349, which is hereby incorporated by reference. This appears to be the basis of Peters® EXCEL® water soluble fertilizers.
Since growers would generally prefer to apply all nutrients at once, and since control of pH is unlikely to be sustainable throughout the fertilizer application processes, there is a need for another approach.
The above problems are resolved in a novel and unobvious manner by the present invention.
Accordingly, a primary object of the invention is to provide a micronutrient and/or macronutrient fertilizer formulation which can resist precipitation and sludge formation, when challenged by such agents as added calcium or magnesium nutrients, or the calcium or magnesium of the local hard water used to dilute the fertilizer or which exists in the growing media.
It is a further object of the invention to minimize sludge in mixing vats and scale buildup in precision fertilizing drip tubes, injectors, and growing media, and to reduce such scale where it already exists.
Another object of the invention is to provide a fertilizer formulation which minimizes loss of nutrient value, and therefor economic value, resulting from use of locally available hard water for solution/dilution, or from the presence of hard water ions in the growing media.
These objects are achieved by the present invention, as taught to those skilled in the art by the present specification and as claimed below.